The first scientific psychologist on the planet was probably named Wilhelm Maximilian Wundt. He created a laboratory in Leipzig 130 years ago (about 20 years after Darwin published "Origin of Species") to scientifically study in internally accessible elements of mental life, taking into account the physiology of the body. My limited understanding of his methods are that his "experimental subjects" were specialists who were highly trained in (1) something like "luminosity" and (2) a technical vocabulary for talking about their introspection.
This research program seems to have had very little effect on the english speaking world. There were few translations. Some of the early stuff may well have been mistranslations. In later decades this research program may have been the "old paradigm" that behaviorists were reacting against when they were going crazy with claims that their own work was "totally reproducible" by virtue of making no reference whatsoever to "internal states of mind"?
If anyone is inclined to read the classics and make accumulative progress the barriers to entry may be substantial... But if anyone is interested, the place to start might be the autotranslation of the german wikipedia article about Wundt, and then there seem to be a few translated books on Amazon by Wundt including:
Sequence index: Living Luminously
Previously in sequence: The ABC's of Luminosity
Next in sequence: The Spotlight
You should pay attention to key mental events, on a regular and frequent basis, because important thoughts can happen very briefly or very occasionally and you need to catch them.
You may find your understanding of this post significantly improved if you read the third story from Seven Shiny Stories.
Luminosity is hard and you are complicated. You can't meditate on yourself for ten minutes over a smoothie and then announce your self-transparency. You have to keep working at it over a long period of time, not least because some effects don't work over the short term. If your affect varies with the seasons, or with major life events, then you'll need to keep up the first phase of work through a full year or a major life event, and it turns out those don't happen every alternate Thursday. Additionally, you can't cobble together the best quality models from snippets of introspection that are each five seconds long; extended strings of cognition are important, too, and can take quite a long time to unravel fully.
Sadly, looking at what you are thinking inevitably changes it. With enough introspection, this wouldn't influence your accuracy about your overall self - there's no reason in principle why you couldn't spend all your waking hours noting your own thoughts and forming meta-thoughts in real time - but practically speaking that's not going to happen. Therefore, some of your data will have to come from memory. To minimize the error introduction that comes of retrieving things from storage, it's best to arrange to reflect on very recent thoughts. It may be worth your while to set up an external reminder system to periodically prompt you to look inward, both in the moment and retrospectively over the last brief segment of time. This can be a specifically purposed system (i.e. set a timer to go off every half hour or so), or you can tie it to convenient promptings from the world as-is, like being asked "What's up?" or "Penny for your thoughts".
When you introspect, there is a lot to keep track of. For instance, consider the following:
You cannot have too much data. (You probably can have too much data in one situation relative to how much you have in another, though - that'll overbalance your models - so make a concerted effort to diversify your times and situations for introspection.) When you acquire the data, correlate it to learn more about what might bring various aspects of your thought into being.